The invention pertains generally to earthworking equipment and more particularly to such equipment in which the working implement is selectively held in different positions with respect to the frame.
It is known that the working implement of various earthworking equipment must be adjusted to meet the requirements of a particular job. For example, in the case of a motor grader, the blade or moldboard is conventionally mounted for a variety of adjustments relative to the frame. The blade is mounted for elevational adjustment, cross slope adjustment, lateral sliding adjustment, and rotational adjustment. Conventionally, the rotational adjustment is achieved by the turning of a "circle gear" in the form of a ring-like structure slidably supported for rotary movement. It will be appreciated that the fit between a circle gear and its bearing support must be loose enough to permit such sliding movement and, as a consequence, a certain amount of wear will occur during the movement of a circle gear. Preferably, the circle gear is locked in position when it is not being rotated to prevent stress in the drive train thereto. Prior art locks or brakes have applied an upward force on the circle gear, thereby raising the blade a distance approximating the amount of wear or looseness.
Modern motor graders use an automatic blade control device for reading the desired grade level from a reference grade line or a wire and automatically adjusting the vertical positioning of the blade to maintain the reference level. However, such devices cannot compensate for changes in the vertical positioning of the blade due to wear in the mating surfaces of the blade support structure and any changes in the vertical positioning of the blade which may occur during adjustment of the angle of the blade with respect to the direction of motion of the motor grader will result in departures from the reference grade level. Since tolerances as small as one-eighth inch are now required in road grading operations, it will be seen that departures from the reference grade level during adjustment of the angle of the blade with respect to the direction of motion of the grader, or the working tolerances and wear inherent in the mounting structures which enable such adjustment of the blade, have made the above mentioned prior art devices unsuitable for such close tolerance work.